1. Field of the Invention
The present invention is directed in general to wireless communication technology. In one aspect, the present invention relates to transformers used with the radio communication transmitters and receivers.
2. Related Art
Communication systems are known to support wireless and wire-lined communications between wireless and/or wire-lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth (BT), advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS) and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device (such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc.) communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over the tuned channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switched telephone network, via the Internet, and/or via some other wide area network.
Wireless communication devices typically communicate with one another using a radio transceiver (i.e., receiver and transmitter) that includes a transmitter section, a receiver section, a transformer for the receiver section, a transformer for the transmitter section, an antenna switch, and an antenna, all or part of which may be incorporated in, or coupled to, the wireless communication device. The antenna receives RF signals that are then coupled to the receiver section by the antenna switch. The antenna also transmits amplified RF signals received from the transmitter section via the antenna switch.
The receiver and transmitter transformers may be implemented as a balun (balanced/unbalanced) transformer which is generally used to convert single ended signals into differential signals and conversely to convert differential signals into single ended signals. For example, RF signals received via the antenna are converted into differential signals, which are provided to a low noise amplifier of the receiver section. Conversely, differential signals from a power amplifier of the transmitter section are converted into single ended signals, which are provided to the antenna.
The transmitter section typically includes a data modulation stage, one or more intermediate frequency stages and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. In direct conversion transmitters/receivers, conversion directly between baseband signals and RF signals is performed. The power amplifier amplifies the RF signals prior to transmission via an antenna.
The receiver section typically includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
In addition to the computational requirements and design complexity for wireless communication systems, such as described above, the ever-increasing need for higher speed communications systems imposes additional performance requirements and resulting costs for communications systems. In order to reduce costs, communications systems are increasingly implemented using Very Large Scale Integration (VLSI) techniques. The level of integration of communications systems is constantly increasing to take advantage of advances in integrated circuit manufacturing technology and the resulting cost reductions. This means that communications systems of higher and higher complexity are being implemented in a smaller and smaller number of integrated circuits. For reasons of cost and density of integration, the preferred technology is CMOS.
Increasingly, the implementation of wireless communication devices as integrated circuit systems has posed design challenges for integrating the inductor components of such circuits. For example, inductors are included in the mixers in the IF stages of both the receiver and transmitter, the power amplifier, a voltage control oscillator of a local oscillation module, the low noise amplifier, and the filters each include one or more inductors. Many attempts have been made to integrate transformers and/or transformer baluns onto radio frequency integrated circuits; however, such integration has been limited due to flux leakage, capacitive coupling limits, and significant series resistance. While these limitations have been partially addressed with transformer IC designs (including coplanar interleaved transformers, toroidal and concentric transformers, overlay transformers and symmetric coplanar transformers), these designs have their own drawbacks. For example, coplanar interleaved transformers suffer from a low quality (Q) factor have small coupling coefficients. Another drawback of conventional power amplifier architecture solutions is that they do not efficiently provide power at all power levels required by differing applications. For example, conventional power amplifier solutions are designed to have maximum efficiency at the highest desired output level, so that when the power level is reduced from its maximum level, the power efficiency is also reduced. As a result, conventional power amplifier solutions do not allow for power output efficiency to be maintained across multiple power levels.
Therefore, a need exists for an improved power amplification method and system for use with radio transceiver circuits in wireless communication devices. In addition, a need exists for a multi-use on-chip transformer that may adjustably provide different inductance values with a small size, optimal shape, high quality factor, reduced resistance and a high coupling coefficient. There is also a need for an improved impedance matching system for use in power amplifier applications whereby power amplifier efficiency is maintained as the power level changes. There is also a need for a power amplification method and system that is capable of performing the above functions and overcoming these difficulties using circuitry implemented in integrated circuit form. Further limitations and disadvantages of conventional systems will become apparent to one of skill in the art after reviewing the remainder of the present application with reference to the drawings and detailed description which follow.